In various industries, such as the dairy, fruit juice, wine, and beer industries, there is a need to assay bacteria and molds. The art does not always distinguish mold assays from bacterial assays when devices for the assay of microorganisms are discussed, but it is known to those skilled in the art that mold assays are often slower than bacterial assays. Methods for detecting low concentrations of mold species typically rely on growth media, such as 3M PETRIFILM™ Yeast and Mold Count Plates or acidified potato dextrose agar. Agar treated with antibiotics, such as chloramphenicol, is also used. These methods take 3 to 7 days to produce a definitive answer, depending on the growth rate of the organism. Food manufacturers in particular desire a faster-responding test, since other growth related test results such as total aerobic (viable) count for bacteria are available within two days, and waiting an extra day or more to get yeast and mold test results is costly. Fluorescence microscopy or flow cytometry may provide a more immediate test result, but these technologies are prohibitively expensive.
The mold species Aspergillus niger is a common fungal food contaminant. Although generally non-pathogenic, it does cause black rot or smut disease on various fruits and vegetables. A. niger is also commonly found in indoor environments, where the colonies can be mistaken for the toxin-producing Stachybotrys mold.
In the viticulture industry, there is a need for improved discrimination between Aspergillus niger and Aspergillus carbonarius. The latter is the primary source in grapes of Ochratoxin A, a mycotoxin that is nephrotoxic, teratogenic, carcinongenic and suppresses the immune system. A. niger and A. carbonarius are difficult to distinguish by eye and are primarily differentiated on the basis of morphology by experienced mycologists using microscopy. Technologies exist to detect Ochratoxin A directly, based on liquid chromatography or immunoassays, but these methods are also costly and require expertise.
Other techniques for the detection of fungi that produce ochratoxin have been pursued. For example, U.S. Pat. No. 7,560,234 (Dobson et al.) putatively describes polymerase chain reaction (PCR) assay techniques that may be used in the detection and/or identification of an ochratoxinogenic fungus.
There is a need for methods that enable rapid detection and discrimination of A. niger and A. carbonarius and related species in a simple, cost effective manner.